I am studying the anatomical and functional organization of the motor neuron pools in the chick spinal cord, and the developmental processes responsible for the establishment of the normal anatomical and functional patterns of connections between motor neurons and muscles. The motor pools supplying individual muscles of the legs and wings have been mapped using intramuscular injections of horseradish peroxidase. In addition, electromyogram recordings of muscle activity during walking and wing flapping are being made in conjunction with videotape recordings of chick movements. This information about normal neuronal connectivity and motor output will be used to evaluate the effects of experimental manipulation of the neurons system in the young embryo. The experimental manipulations which have been or which will be studied include: grafting an additional leg or wing, producing experimental duplications or deletions of particular limb segments, substituting brachial for lumbar spinal segments and vice versa, deafferenting the spinal cord by neural crest removal and abolishing descending information from the brain by spinal cord transection.